Hairpieces of various types using a network as the wig base have been known in the past. A wig base having a locally-disposed network is comprised, as shown in Japanese Utility Model Preliminary Publication No. Sho 58-176926 filed by the present applicant, of: a hair-dividing region made of a plastic sheet for giving an external appearance as if of the user's own skin; a central net portion; and a reinforcing support portion, and these region and portions are anchored to each other by a specific means. Also, a hairpiece such that the entire wig base is constructed by a network is disclosed in, for example, U.S. Pat. No. 3,905,378.
The materials of the network which are used in these prior techniques are usually nylon monofilaments, and the monofilament is shaped into a network by welding. According to the method of said U.S. patent, a hairpiece is manufactured, for example, by placing a first plane which is comprised of a group of warps made of nylon filaments of a diameter of 0.005 inch and disposed in the plane with a filament-to-filament spacing of 0.05 inch, upon a second plane consisting of a group of wefts of likewise-disposed nylon filaments crossing at right angles the group of warps, with these two groups of filaments not being woven into each other, and by welding, by relying on an ultrasonic wave heating while maintaining the state of the planar pattern, the respective points of intersection of the monofilaments which cross each other at right angles, thereby forming a planar non-woven nylon network; thereafter using a head-contoured male mold which closely conforms to the user's head contour and which has been sorted out in advance from among several different kinds of heatable models of head-contoured male molds, and pressing and drawing said planar non-woven nylon network against said head-contoured male mold while heating, thereby preliminarily shaping it so as to present the contour of the head portion; cutting it into a required contour and dimension; and thereafter securing hair fibers to said welded sites, whereby a hairpiece is manufactured. In case a net base is constructed according to the above-mentioned method, the non-woven network which originally has been formed into a planar shape is markedly deformed or drawn by both the heat and the physical coercive force applied thereto during the abovesaid preliminary shaping process, and thus it eventually presents various uneven mesh pattern regions depending on the individual sites. Although the network is shaped temporarily into a substantially same shape as that of the heat-contoured male mold due to heat-setting, the nylon filaments which are made of a thermoplastic resin have the tendency to restore their original shape with the passage of time, so that they will either restore their originally shaped pattern of crossing at right angles owing to said tendency and also to the welding force applied at the right-angle crossings at the points of intersection of the warp and weft filaments, or they will go so far as to cause a breakage at the welded sites. Not only that, even when a plurality of head-contoured male molds are prepared beforehand, the contour and dimension of the user's head is such that there is wide variation per individual persons, and thus it is not always possible to manufacture a wig base made of a network having such contour and dimension as are in substantial agreement with the head contour of each individual user.